Brussels has warned the government negotiations can't start next month unless an agreement is reached.

A final decision on the Irish border cannot be made until Britain and the European Union have agreed a trade deal, Liam Fox said on Sunday (26 November).

Speaking on Sky News's Sunday with Niall Paterson, the Secretary of State for International Trade said there needed to be clarity over the future trading relationships between Britain and the EU before the debate over the Irish border could be settled.

"We have always had exceptions for Ireland, whether it's in our voting rights, our rights of residence in the UK, we have always accepted a certain asymmetry and that will have to be part of whatever agreement we come to with the European Union," he said.

"But we can't come to a final answer to the Irish question until we get an idea of the end state.

"And until we get into discussions with the EU on the end state that will be very difficult, so the quicker that we can do that the better, and we are still in a position where the EU doesn't want to do that."

Fox's stance is in stark contrast with the EU's, as Brussels has previously insisted the issue of the Irish border needs to be addressed before formal talks can resume at a summit next month.

The Irish government is understood to be deeply unsatisfied with the options put forward so far to prevent a hard border between the Republic and Northern Ireland from being installed. Dublin believes the only feasible way to do so is to keep Northern Ireland within the customs union, an option Fox appeared to categorically rule out on Sunday.

"We don't want there to be a hard border, but the UK is going to be leaving the customs union and the single market," he said.

Leo Varadkar, the Irish prime minister has demanded a written guarantee that the hard border between the two counties will not be restored once the UK leaves the EU and Phil Hogan, Ireland's EU commissioner, reiterated Dublin will "continue to play tough to the end" over its threat to veto trade talks without border guarantees.

"If the UK or Northern Ireland remained in the EU customs union, or better still the single market, there would be no border issue," he was quoted as saying by The Observer.

"That's a very simple fact. I continue to be amazed at the blind faith that some in London place in theoretical future free trade agreements."

Meanwhile, John McDonnell, the shadow chancellor, expressed concerns at Fox's comments, hinting they could put negotiations between Britain and the EU in jeopardy.

"The one thing that we don't want to do is jeopardise any movement quickly, because we need movement to enable us to get into the proper trade negotiations," he told ITV's Peston on Sunday. "So I'm hoping that isn't a Downing Street-sanctioned statement that's he's made."